This invention relates generally to an implanted cardiac pacer and more particularly, it relates to a method and apparatus for calibrating internal measurements of an implanted cardiac pacer by "software trims".
Heretofore, when resistive components are required to be used in conjunction with hybrid integrated circuits, external resistor elements were connected by external wires to the integrated circuits. In order to overcome this disadvantage, resistive values have been plated directly to the ceramic substrate during the manufacturing of the hybrid integrated circuits. The plated material is generally in the form of a hardened resistive ink. Since these plated resistors on the hybrid integrated circuit are required to be of a precise value, they are checked in the manufacturing process and then are trimmed mechanically to the desired value if they are found to be inaccurate. Typically, this is achieved by the use of a laser beam or other mechanical means for removing a portion of the plated resistive material.
It would therefore be desirable to provide means for avoiding the necessity of mechanically trimming the resistors on the hybrid integrated circuits after manufacturing. The present invention provides a means for calibrating internal measurements of an implanted cardiac pacer by using a series of calibration measurements which are performed during the manufacturing process. Specifically, these internal measurement results are compared to the correct values obtained from a precise external instrument and correction factors are computed. The correction factors are then programmed into the pacer to be stored in a dedicated random-access memory (RAM) device. When an external programmer/receiver commands via telemetry the reading of the uncorrected or raw internal measurements, there will be telemetered from the implanted pacer these internal measurements accompanied along with correction factors for each respective measurement. The programmer/receiver includes a read-only memory (ROM) for storing an algorithm programmed therein and a microprocessor for computing corrected measurement values for visual display.